Recently, in a radio communication system such as WiMAX (worldwide interoperability for microwave access), for example, the orthogonal frequency division multiplexing (OFDM) scheme has been used in order to utilize radio resources more efficiently. In addition, adaptive array control by an adaptive array antenna has also been introduced in such radio communication system.
In the adaptive array control, an array weight used to form a beam of a radio signal to be transmitted to a communication destination is calculated based on “known information” included in a radio signal received from the communication destination (a mobile station, for example).
In addition, in the OFDM scheme, a symbol string in which multiple symbols are arranged in a time axis direction and a frequency axis direction (subcarrier direction) is used. Generally, the symbol string includes: preamble symbols used in symbol synchronization and calculation of an array weight; and data symbols used in transmission of user data.
For a case where the adaptive array control is introduced in a radio communication system to which the OFDM scheme is applied as described above, there has been known a method in which the preamble symbol part and the data symbol part of known information used to calculate an array weight is changed in order to calculate the array weight more accurately (Patent Document 1, for example).
Patent Document 1: JP-A 2002-185375 (pages 6 to 7, FIG. 2)